Oven control system including single-dial control

ABSTRACT

A single-dial oven control is provided for a heat-cleaning oven in which rotation of the dial throughout the greater portion of its rotatable range covers the normal cooking temperature range, with rotation to a point in the remaining part of the rotatable range setting the control for a heat-cleaning operation in the oven. The control includes switch means connected directly in series with the electrical heating means in the oven and incorporates an arrangement for converting linear rotational motion of the user-operated shaft into nonlinear axial motion of means for changing the temperature setting.

United States Patent Holtkamp [54] OVEN CONTROL SYSTEM INCLUDING SINGLE-DIAL CONTROL [72] Inventor: Calvin J. lloltkamp, Mansfield, Ohio [73] Assignee: Westinghouse Electric Corporation, Pittsburgh, Pa.

[22] Filed: Dec. 31, 1970 [21] Appl. No.: 103,098

[52] U.S.Cl ..2l9/4l3, 219/398, 219/489, 337/312, 337/323, 337/330 [51] Int. Cl ..F27d 11/02 [58] Field ofSearch ..219/412,413, 393, 398, 396, 219/489; 337/115, 312, 313, 319, 323, 330

[56] References Cited UNITED STATES PATENTS 2,935,591 5/1960 Lee ..219/398 2,993,969 7/1961 Alcott ..337/3l2 3,214,539 10/1965 Glaberson et a1. .....219/398 X [151 3,648,012 [451 Man 7, 1972 3,387,874 6/1968 Holtkamp.... .219/413 X 3,410,988 11/1968 Nagel 1 ..2l9/412 3,461,415 8/1969 Dahlgren ..219/4l3 X 3,549,862 12/1970 Holtkamp ..2l9/4l3 X 3,569,670 5/1971 Eff ..2l9/4l3 Primary ExaminerVolodymyr Y. Mayewsky AttorneyF. l-l. Henson and E. C. Arenz [5 7] ABSTRACT A single-dial oven control is provided for a heat-cleaning oven in which rotation of the dial throughout the greater portion of its rotatable range covers the normal cooking temperature range, with rotation to a point in the remaining part of the rotatable range setting the control for a heat-cleaning operation in the oven. The control includes switch means connected directly in series with the electrical heating means in the oven and incorporates an arrangement for converting linear rotational motion of the user-operated shaft into nonlinear axial motion of means for changing the temperature setting.

7 Claims, 12 Drawing Figures CLOCK SELECTOR SWITCH LOCK ASSY Patented March 7, 1972 4 Sheets-Sheet 2 FIG. 4

Patented March 7, 1972 I 4 Sheets-Sheet FIG. 7

FIG; 6

FIG. 9

Z CAM SLOPE REF. LINE L BROIL OFF CLEAN FIG. IC)

BAKE

FIG. lI

CLOCK o--ooo- R ABRRO SELECTOR JSWITCH 8TB RO BR ABR 4 Sheets-Sheet 4 gocx ASSY Patented March 7, 1972 OVEN CONTROL SYSTEM INCLUDING SINGLE-DIAL CONTROL CROSS-REFERENCE TO RELATED PATENT APPLICATIONS My copending U.S. Pat. application Ser. No. 103,097, W. E. Case 40,656) is considered to be a related patent application.

BACKGROUND OF THE INVENTION IField of the Invention The invention pertains to the art of temperature control of heat-cleaning ovens.

2. Description of the Prior Art It is conventional and well known to provide, in an oven control system for the ordinary oven which does not accommodate a high-temperature heat cleaning operation, a singledial hydraulic oven control including two basic parts; an adjustable thermostatically controlled switch mechanism and a circuit selector switch, both controlled by a common shaft. In addition to an optional OFF position, bake circuitry is automatically set up throughout the adjustable bake temperature range, and broil circuitry is automatically set up at the highest temperature point. The adjustable thermostatically controlled switch mechanism includes a snap-acting, overcenter mechanism for operating the cycle switch and which is operated in turn by a hydraulically filled oven sensor bulb. The oven temperature is set by the adjustment of the dial shaft, threaded through a bushing, which positions the overcenter mechanism at the proper position. The circuit selector switch consists of conventional cam-operated spring blades which cooperate with mating contact terminals. The temperature limit of the control is determined by the fluid used in the hydraulic bulb. Chlorinated diphenol fluid is typically used in controls that are designed for nonself-clean ovens, while liquid mercury, or alternatively, a sodium potassium alloy, may be used for high-temperature self-clean ovens. The thread pitch on the shaft is matched to the expansion characteristics of the fluid used so that the usable temperature zone is dispersed over a suitable dial angle, which is generally as extensive as possible for temperature setting repeatability.

One typical dial layout for a hydraulic control used only for bake and broil functions, on either type of oven, uses 335 angular degrees of dial rotation to cover the 460 temperature degree spread required (140 to 600 F.), and uses 25 angular degrees for the rotational shaft stop. The 335 angular degrees is divided as follows: 265 angular degrees for the bake zone (140 to 525 F.) and 70 angular degrees for the space required to obtain the approximate 600 F. broil temperature position. The single-dial version of this control which contains circuit-sensing switches is designed to have an OFF position in the 70 angular degree zone between bake and broil. U.S. Pat. No. 2,935,591, generally illustrates the functional components of an oven control of the type just described for a nonself-clean oven.

If the control is attempted to be modified for use over a 900 F. temperature spread l40 to l,040 F.) through selection of the proper shaft thread, it is apparent that the bake and broil zones will be compressed approximately 50 percent and the substantially nonuseful zone between 600 and I,040 F. will be excessively wide and generally unsatisfactory.

One oven temperature control which is currently on the market and may be used for baking, broiling and cleaning through operation of a single shaft is produced by the King Seely Corporation. This control is considered to have a number of disadvantages in certain respects including a design which apparently will not permit full current for the ovenheating elements to be carried through its internal contacts so that a heater-operated relay is required to be used in conjunction with the control. The purpose of the relay is of course to control the main switch contacts which carry the full current for the over heater elements. This control is considered to present some calibration problems. Also, it is noted that while a single shaft is used to set any of the bake temperatures, the

broil temperature and the clean temperature, the arrangement requires that the shaft be pushed in fully, then rotated slightly and released in setting a clean temperature so that a yoke carried at the rear end of the shaft maybe seated about a stop bracket on the rear face of the control casing. Of course, to change the setting back to a bake or a broil setting, the shaft must again be pushed in and rotated to release the yoke from the stop brackets.

The aim of my invention is to provide a single-dial oven control and system which in large part utilizes the standard oven control, and which avoids at least some of the disadvantages of the noted single dial oven control currently on the market.

SUMMARY OF THE INVENTION In accordance with the invention, the control system incasing and connected in series in the power circuit with the heating means in oven, positionable means and oven temperature responsive means both cooperating with the overcenter mechanism to control the temperature setting at which the oven temperature responsive means effects the cycling of the switch means, a rotatable shaft for setting the thermostat by moving the positionable means in accordance with the shaft rotation through an arrangement which includes cam means, and rotatable, axially movable cam follower means carrying the positionable means, with the cam means including a cam face having a relatively gradual slope throughout its major extent to provide relatively gradual axialmovement of said positionable means to correspond with the range of cooking operation temperatures, and having a relatively steep slope throughout a minor extent to provide a relatively greater axial movement of said positionable means to a position corresponding with a cleaning operation temperature.

Additionally, numerous structural features are provided to facilitate the calibration and the manufacturing and reliability aspects of the control.

DRAWING DESCRIPTION FIG. 1 is a face view of a thermostatic oven control according to the invention with the front cover removed;

FIG. 2 is a vertical section corresponding to one taken along the line IIII of FIG. I, but with the front cover in place;

FIG. 3 is a face view of the rear of the thermostat, but with the rear cover and other parts omitted for purposes of clarity;

FIG. 4 is a side view, partly broken and partly in section of a cam and shaft arrangement for the thermostat;

FIG. 5 is a front face view of the cam and shaft of FIG. 4;

FIG. 6 is a front view of the cam follower assembly for the thermostat;

FIG. 7 is a side view of the assembly of FIG. 6;

FIG. 8 is a front face view of the cam bushing for the thermostat;

FIG. 9 is a side view of the cam bushing of FIG. 8;

FIG. 10 is a graphical representation of the cam face slope in developed form;

FIG. II is a face view of an indicated dial for the thermostat; and

FIG. 12 is a schematic view of the circuit for an oven control system in which the thermostat may be used.

BRIEF DESCRIPTION OF PREFERRED EMBODIMENT contains the overcenter mechanism, cycling switch means and associated parts which control its operation.

The relative locations of the contact terminals on the exterior of the thermostat by which the thermostat is connected into circuits in which it functions, is best seen in FIG. 3, the exterior terminals being identified as l, 2, 4, 5, 6 and 7 to correspond with the terminal indicia to be provided on proposed commercial thermostats. While the terminals are only visible from the rear side of the casing, the corresponding location of the terminals as viewed from the front is shown in FIG. 1 to aid in relating the location of the contacts as viewed from the front of the thermostat. The electrically conductive strips which terminate in the exterior terminals are riveted to the casing and are given the same numeral with a suffix letter a" to indicate the electrically common connection. The switch contact portion of each terminal and strip also carries the same numeral with a suffix b. Thus for example, and referring to FIG. I, the exterior terminal 4 is electrically the same as the strip 4a riveted to the casing intermediate wall 11, with the strip 4a carrying a contact 4b thereon. In the case of the exterior terminals 1 and 2, only the rivets therefor are seen in FIG. 1, while the contact strips 1a and 2a carrying the contact terminals with the b suffixes are seen in FIG. 3.

Contact spring arms 8 and 9 are located in the front chamber 12. Spring arm 8 is anchored at its upper end and carries a movable contact 8b at its lower end. Spring arm 9 is also anchored at its upper end and carries contact 9b at its lower end. Cam faces 16a and 16b on the cam generally designated 16 move the spring arms 8 and 9 in accordance with rotation of the cam 16 so that contact 8b is moved into or out of engagement with contact 4b, and contact 9b is movable into and out of engagement with either contact 6b or 7b in accordance with whether the operation is to be cooking or cleaning. The fixed upper ends of the spring arms 8 and 9 extend through slots in the intermediate wall 11 and have portions 8a and 9a riveted to the intermediate wall (FIG. 3). Additional contacts 8c and 9c are provided on these riveted portions.

Referring now to FIGS. 2 and 3, the cycling switch arrangement generally designated 17 includes a pair of electrically conductive bridging strips 18 (only one as seen in FIG. 2) carried in spaced-apart electrically insulated relation by the plastic carrier 19 upon which they are secured in loosely held relation to accommodate proper seating upon the contacts. When the cycling switch is closed, the one strip bridges from contact 2b (FIG. 3) to Be, while the other bridges from 1b to 9c. The carrier 19 is attached to a spring arm 20 which has a lower T-shaped end 21 which seats in a niche 22 formed in the casing material. The upper end of the arm 20 is received in an indent at one end of a curved overcenter spring 23 which has a dimple 24 at its opposite end seating on the point of an adjusting screw 25 turned into the top wall of the casing. The arm 20 is fulcrumed at one location against the end of movable shaft 26. The pressure wafer 27 connected by capillary tube 28 to an oven temperature sensitive bulb (not shown) bears against the spring arm 20 at a location between the shaft 26 fulcrum location and the lower end 21.

The general way in which the cycling switch 17 works is as follows as viewed in FIGS. 2. With an increase in oven temperature the pressure wafer exerts a correspondingly increasing force to the left on arm 20 at the bearing location. When the force and lever arm product provided by the pressure wafer exceeds the force exerted by the overcenter spring 23 urging the carrier 77 to the left, the overcenter spring 23 snaps the cycling switch carrier 17 to the right until stopped by the inwardly projecting prongs 29 carried by the rear cover 15.

' Thus the switch is opened. As the temperature in the oven decreases below a given temperature, the pressure wafer retreats with the slightly bowed spring arm 20 following so that at a given point it will cause the carrier to snap back to close the cycling switch. It will be appreciated that my moving the shaft 26 in an axial direction, the temperature setting of the thermostat may be changed.

It is noted that the general arrangementiof the cycling switch with overcenter snap action, with its operation being controlled by the relationship between user operated positionable means as shaft 26 and pressure wafer 27 is not new. Nor is it new to provide the circuit-selecting arrangements with the spring arms 8 and 9 and the contact terminal arrangement as previously described. In fact, the invention to be described hereinafter is intended to take advantage of this established design by incorporating modifications and changes therein relating to the manner in which movement of the shaft 26 is accomplished.

In accordance with the invention, axial movement of the shaft 26 is attained through rotation of the user shaft 30 through the medium of the mechanism including the rotatable cam 16, a rotatable and axially movable cam follower generally designated 31, and a fixed cam bushing generally designated 32.

Referring now to FIGS. 4 and 5 in connection with FIG. 2, the cam 16 and the shaft 30 assembly includes the shaft 30 rigidly fixed to a generally cup-shaped member 33 through a disc 34 which is secured to the cup 33 by rivets 35 passing through three of four equally spaced holes adjacent the periphery of the disc 34. The fourth of the rivet holes is left open to permit the insertion of a tool for an adjustment to be later described. At opposite sides on the interior wall of the cup 33, axially extending grooves 36 and 36a are provided on the walls, the one groove 36a being slightly wider than groove 36 as may be seen by the dashed line representation of the location of these grooves in FIG. 1. The purpose of these grooves is to receive the opposite ends of projecting parts on the cam follower member 31, which will now be described in connection with FIGS. 6 and 7.

The cam follower 31 and shaft 26 assembly is arranged to move axially in accordance with rotational movement of the cam cup 16. As viewed from the front, the cam follower has the general outline of a cross with upper leg 37 and lower leg 38 having rearwardly directed flanges 37a and 38a, the radial dimension from the center of the shaft 26 to the outer circumference of the flanges being approximately the same as the interior radial dimension of the cam cup 16. The distance between the center of the shaft 26 and the outer ends of the side arms 39 and 40 is greater than that radius so that the ends of the side arms 39 and 40 are slidably received within the grooves 36 and 36a of the cam cup 16. The exterio'rly threaded end 26a of the shaft 26 is turned into an interiorly threaded hold in the general center of the cam follower with a tension nut 41 being turned up sufficiently tightly against the rear face of the cam follower as to secure the shaft 26 to the cam follower 31 while permitting adjustment of the shaft 26 relative to the cam follower by using a screwdriver in the slotted end of the part 26a. The lower leg 38 of the cam follower 31 includes an opening 42a adjacent the extremity of the leg. The rear end of the flange 38a is provided with a radially inward directed tab 42 which is the cam follower part which bears against the cam face to be described in connection with FIGS. 8 through 10.

The cam bushing generally designated 32 and providing a cam face for the cam follower part 42 to ride against, is shown in FIGS. 8 and 9 as a separated part and substantially enlarged relative to FIGS. 6 and 7, and as an assembled part in FIG. 2. The cam bushing as the general form of a half spool. The enlarged end part 43 has an outer diameter which permits it to be accommodated within the inner diameter between the flanges 37a and 38a of the cam follower 31 so that the cam follower 31 may rotate freely about the stationary cam bushing 32. The rear end face 44 of the part 43 provides a cam face against which the tab 42 of the cam follower assembly bears. The cam face begins at the radial line x (FIG. 8) and extends for approximately 230 angular degrees to the radial line k at a relatively gradual slope of about 0.023-inch differential as measured in an axial direction relative to the cam bushing. For the next 20 angular degrees from radial line k to radial line y the slope is absent or may be minimal. For the next 86 angular degrees to the radial line 2, the slope is relatively steep and provides an axial differential of 0.022 inch. At a location 45, which is 72 angular degrees from the radial line y, a threaded hole is provided to receive a heat-cleaning temperature adjusting screw, also identified as 45. The angular segment of 24 between radial line z and radial line x is left open to permit the assembly of the cam follower 31 to the cam bushing, the opening permitting the tab 42 to be moved into its position to bear against the cam face of the cam bushing end 43.

The smaller diameter end 46 of the cam bushing is provided with a relatively thin rim portion which is turned over against the casing intermediate wall 11 (FIG. 2) to fix the cam bushing to the intermediate wall and hold it against movement in either an axial or a rotational direction. The cam bushing is provided with a central bore 47 which accommodates the shaft 26 of the cam follower assembly in freely slidable relation.

The profile of the cam face in developed form is shown in FIG. in which Figure, as well as in FIG. 8, the segments of the cam face relating to a bake operation, a broil operation and a clean operation are indicated by the legends.

Referring again to FIG. 2, the cam cup 16, the cam follower assembly 31, and the cam bushing assembly 32 are shown in their assembled form in the thermostat casing. When shaft 30, which carries the indicating dial of FIG. 11 thereon for rotation therewith, is rotated to set an oven temperature, the cam cup 16 is rotated therewith and causes the cam follower assembly 31 to rotate also because of the engagement of the ends of arms 39 and 40 (FIG. 6) engaging the interior grooves 36 and 36a of the cam cup 16. Since the cam follower 31 includes the shaft 26 as part of a rigid assembly, with the arm 20 (FIG. 2) of the cycling switch assembly bearing against the end of the shaft 26 so as to constantly exert a leftward force on the shaft 26 as viewed in FIG. 2, the tab 42 serving as the cam follower part bears against the cam face 44 of the cam bushing assembly 32. Thus as the cam follower assembly 31 rotates, it is also moved axially in accordance with the slope of the cam face 44 and the degree of rotation of the cam follower assembly.

The thermostat in FIG. 2 is shown with its parts positioned to correspond with the thermostat being set for a cleaning operation. In this position, the empty rivet hole 35 of the cam cup 16 is in alignment with the aperture 41 of the cam follower assembly 31 so that an instrument may be inserted through these aligned holes to adjust the setting of the screw 45. This factory or service adjustment moves the screw 45 axially to set the particular temperature at which the cleaning operation is to occur. For the calibration of the thermostat for cooking operations, a tool is inserted through the hollow user shaft 30 to rotate the shaft 26 relative to the cam follower 31 as a whole.

It will be appreciated that by moving the shaft 26 to the left as shown in FIG. 2, either through calibration or through normal operation of the user shaft, the fulcrum for the arm 20 of the cycling switch assembly is accordingly moved to the left and a greater force to the left by the pressure wafer 27 is required to cause the overcenter mechanism to snap the cycling switch to open position. Translating this to terms of the user setting the thermostat, as the user shaft is turned through the total 250 angular degrees encompassing the cooking operation the cycling temperature of the thermostat is gradually moved through a total of about 460 F.; from 140 F. to the broil temperature of 600 F. Through the remaining 72 angular degrees from the broil setting to the clean setting with the cam follower tab 42 centered on the adjustment screw 45, the substantially steeper slope of the cam face 44 corresponds to a change in degrees of temperature from 600 to approximately 1,040 F., which is the currently preferred cleaning temperature. It is noted that the cam face is designed so that in the usual calibration case, the high-temperature adjustment screw 45 will project slightly out of the cam face to permit accommodating manufacturing variances in parts. From the foregoing, it will be appreciated that the angular degrees of dial rotation in the order of a ratio of 3 to l to encompass the cooking operation temperatures as contracted to the dial rotation to move to'a cleaning operation temperature setting.

Turning now to FIG. 12, the incorporation of the described thermostat in an oven control system in accordance with the invention and the circuit arrangement therefor is shown. The major components of the system in addition to the thermostat 10 include the selector switch 48, a lock assembly 49 for the purpose of insuring that a cleaning operation cannot occur without the oven door being locked during the high-tempera ture operation, the bake heating element 50, broil heating element 51, and optional auxiliary broil heating element 52, all the heating elements of course being located within the oven (not shown). For purposes of understanding the invention, it is considered unnecessary to detail the particular circuits which are energized in all of the various cooking operations and the cleaning operations. However for those who would desire .to trace the circuitry, alphabetical indicia are located adjacent each of the contacts to indicate that in particular cooking or cleaning operation the contacts are closed. These indicia and their meaning are as follows: B-bake; TB-time bake; BR-broil; A BR-auxiliary broil; RO-rotisserie; C L-clean. For example, when the selector switch 48 is set to bake, and the user shaft 30 of the thermostat 10 at any temperature in the bake range, all of the contacts with the initial B will be in closed position. With the selector switch 48 set to a cleaning position and the user shaft turned to a cleaning position, those contacts carrying the legend CL will be closed. Rotation of the cam 16 of the thermostat 10 sets up the required switch closing (8b to 4b and 9b to either 6b or 7b) inside the thermostat.

It will be especially noted that the cycling switch contacts 18, controlled in turn by the pressure wafer 27 responsive to oven temperatures, is connected directly in series with the heating elements in the oven for the various operations. This is in contrast to' an arrangement in which the thermostat cycling switch controls a relay, which in turn controls the energization of the heating element in the oven. While the circuit connections in the bake, broil and cleaning operations will not be traced as such, it is noted that it may be derived from the schematics that in the bake operation the bake element 50 is directly across opposite sides of the usual three-wire line, while the broil element 51 is between one side of the line and neutral. In the broil setting, the broil element 51 is directly across opposite sides of the line. In the cleaning operation, and in accordance with the preferred manner of operation, the broil element 51 alone provides all of the heat necessary for the cleaning operation, with the bake element being deenergized. It will be appreciated that other arrangements for purposes of providing heat during the cleaning operation may be provided by changing the circuit.

One particular advantage of the oven control thennostat according to the invention, as distinguished from the type of oven control thermostat which utilizes a thermal relay to control the power to the heating elements in the oven, is attained in connection with broiling operations by virtue of avoiding cycling of the broil element during broiling. This advantage is perhaps best understood by considering the nature of the type of oven control thennostat which utilizes a separate thermal relay, and typically uses a creep action contact arrangement, as distinguished from a snap-acting contact arrangement. It is well understood that in cooking operations for a particular temperature, that the heating elements nonnally cycle on and off with the oven temperature overshooting and then subsequently undershooting on opposite sides of the desired temperature. If it is assumed that the overshoot and undershoot temperature is about 50, in the normal cooking range, excluding broiling, there is no substantial difference in the operation of a snap-acting versus a creep-acting switch closing arrangement. However, in a broil operation it is desirable that the broil element be continuously energized, with a set point of 600 F. With the type of thermostat utilizing a relay, the thermostat contacts open at 600 F. so that the thermal lag of the relay (about 20 seconds) will keep the overshoot and undershoot oven temperatures within a reasonable range. In other words, when the oven temperature reaches 600' F. with the type of thermostat using a thermal relay, the contacts in the thermostat open and seconds later the broil element will be deenergized and remain deenergized until the oven temperature drops to 600 F., at which time the thermal lag of the relay will again enter the picture and permit the oven to drop further to, say, 550 F. before the heating element is again energized. Since there is essentially no thermal lag involved with a snap-acting thermostat according to the inven tion, in a broiling operation therewith the oven temperature can reach up to 650 F. without the broil element being deenergized. In practice where broiling occurs with the door open, the broil element will remain energized without the oven exceeding the 650 F. so that the superior broiling obtained with the constant energization of the broiling element is obtained.

I claim:

1. An oven and oven control system including a thermostat for a self-cleaning pyrolytic oven in which the oven includes heating means therein for both cooking operations, and a cleaning operation, comprising:

power circuit means including said heating means therein;

a casing for said thermostat;

switch contact means located in said casing and being connected in series in said power circuit means for directly controlling energization of said heating means;

a snap-acting, overcenter mechanism for operating said switch contact means;

oven temperature responsive means associated with said mechanism to move said mechanism in accordance with changes in oven temperature;

axially positionable means associated with said mechanism for adjusting the operating point of said mechanism;

oven user rotatable means for controlling the axial position of said positionable means;

said user rotatable means including means for converting rotational motion to axial movement of said axially positionable means and for moving said axially positionable means a substantially greater distance for a given degree of rotation of said user rotatable means in a minor part of the rotational range of said user rotatable means than the distance said axially positionable means is moved for the same degree of rotation throughout the major part of the rotational range to permit moving said axially positionable means to an oven-cleaning temperature setting from maximum oven-cooking temperature setting by rotating said rotatable means through a minor part of the rotatable range of said rotatable means.

2. An oven and oven control system according to claim 1 wherein:

said oven user rotatable means includes a rotatable and axially movable cam follower means carrying said axially positionable means, and a stationary cam bushing presenting a cam face for said cam follower means therein.

3. An oven and oven control system according to claim 2 wherein:

said cam face includes a relatively gradual slope throughout its major extent to provide a relatively gradual axial movement of said positionable means therethrough to correspond to said cooking operations, and provides a substantially greater slope to provide a substantially greater axial movement of said positionable means to a given position in its remaining extent to correspond with said cleaning operation.

4. An oven temperature control thermostat for controlling oven temperatures during both cooking operation and a heatcleaning operation, comprising:

a casing;

operating said switch contact means; means in said casing positionable relative to said overcenter mechanism for setting the operating point of said mechanism;

oven temperature responsive means for operating said overcenter mechanism in accordance with oven temperatures sensed relative to the temperature setting to which said positionable means is positioned;

a rotatable shaft for setting said thermostat;

means for moving said positionable means in accordance with shaft rotation;

said moving means including cam means, and rotatable, axially movable cam follower means carrying said positionable means;

said cam means including a cam face having a relatively gradual slope throughout its major extent to provide relatively gradual axial movement of said positionable means to correspond with a range of cooking operation temperatures, and having a relatively steeper slope throughout a minor extent to provide a relatively greater axial movement of said positionable means to a given position to correspond with a cleaning operation temperature.

5. An oven and oven control system including a thermostat for a self-cleaning pyrolytic oven having heating means therein for both cooking operations and a cleaning operation, comprising:

power circuit means including said heating means therein;

a casing for said thermostat;

switch contact means in said casing and being connected in series in said power circuit for directly controlling energization of said heating means;

a snap-acting, overcenter mechanism for operating said switch contact means;

means responsive to oven temperatures for exerting forces upon said mechanism in accordance with changing oven temperatures;

axially positionable means bearing against said mechanism to adjust the temperature which said oven temperature responsive means causes said mechanism to operate said switch contact means between open and closed positions;

means to position said axially positionable means including,

a rotatable and axially movable cam follower means carrying said axially positionable means;

a stationary cam bushing presenting a cam face for said cam follower means to bear against;

rotatable shaft means connected to effect rotation of said cam follower means to move said cam follower means along said cam face to obtain said axial movement of said cam follower means and accordingly said positionable means;

said cam face providing a relatively gradual axial movement of said positionable means throughout its major extent to correspond with said cooking operations; and

providing substantially greater axial movement of said positionable means to a given position in its remaining extent to correspond with said cleaning operation.

6. An oven and oven control system according to claim 5 wherein:

said cam bushing includes means adjustable in an axial direction relative to said cam bushing at a location on said cam face to correspond with said cam follower means being in a cleaning operation position.

7. An oven and oven control system according to claim 5 including:

means for adjusting the position of said axially positionable means relative to said cam follower means independently of rotation of said cam follower means to permit calibration of said thermostat. 

1. An oven and oven control system including a thermostat for a self-cleaning pyrolytic oven in which the oven includes heating means therein for both cooking operations, and a cleaning operation, comprising: power circuit means including said heating means therein; a casing for said thermostat; switch contact means located in said casing and being connected in series in said power circuit means for directly controlling energization of said heating means; a snap-acting, overcenter mechanism for operating said switch contact means; oven temperature responsive means associated with said mechanism to move said mechanism in accordance with changes in oven temperature; axially positionable means associated with said mechanism for adjusting the operating point of said mechanism; oven user rotatable means for controlling the axial position of said positionable means; said user rotatable means including means for converting rotational motion to axial movement of said axially positionable means and for moving said axially positionable means a substantially greater distance for a given degree of rotation of said user rotatable means in a minor part of the rotational range of said user rotatable means than the distance said axially positionable means is moved for the same degree of rotation throughout the major part of the rotational range to permit moving said axially positionable means to an ovencleaning temperature setting from maximum oven-cooking temperature setting by rotating said rotatable means through a minor part of the rotatable range of said rotatable means.
 2. An oven and oven control system according to claim 1 wherein: said oven user rotatable means includes a rotatable and axially movable cam follower means carrying said axially positionable means, and a stationary cam bushing presenting a cam face for said cam follower means therein.
 3. An oven and oven control system according to claim 2 wherein: said cam face includes a relatively gradual slope throughout its major extent to provide a relatively gradual axial movement of said positionable means therethrough to correspond to said cooking operations, and provides a substantially greater slope to provide a substantially greater axial movement of said positionable means to a given position in its remaining extent to correspond with said cleaning operation.
 4. An oven temperature control thermostat for controlling oven temperatures during both cooking operation and a heat-cleaning operation, comprising: a casing; switch contact means in said casing; a snap-acting, overcenter mechanism in said casing for operating said switch contact means; means in said casing positionable relative to said over-center mechanism for setting the operating point of said mechanism; oven temperature responsive means for operating said overcenter mechanism in accordance with oven temperatures sensed relative to the temperature setting to which said positionable means is positioned; a rotatable shaft for setting said thermostat; means for moving said positionable means in accordance with shaft rotation; said moving means including cam means, and rotatable, axially movable cam follower means carrying said positionable means; said cam means including a cam face having a relatively gradual slope throughout its major extent to provide relatively gradual axial movement of said positionable means to correspond with a range of cooking operation temperatures, and having a relatively steeper slope throughout a minor extent to provide a relatively greater axial movement of said positionable means to a given position to correspond with a cleaning operation temperature.
 5. An oven and oven control system including a thermostat for a self-cleaning pyrolytic oven having heating means therein for both cooking operations and a cleaning operation, comprising: power circuit means including said heating means therein; a casing for said thermostat; switch contact means in said casing and being connected in series in said power circuit for directly controlling energization of said heating means; a snap-acting, overcenter mechanism for operating said switch contact means; means responsive to oven temperatures for exerting forces upon said mechanism in accordance with changing oven temperatures; axially positionable means bearing against said mechanism to adjust the temperature which said oven temperature responsive means causes said mechanism to operate said switch contact means between open and closed positions; means to position said axially positionable means including, a rotatable and axially movable cam follower means carrying said axially positionable means; a stationary cam bushing presenting a cam face for said cam follower means to bear against; rotatable shaft means connected to effect rotation of said cam follower means to move said cam follower means along said cam face to obtain said axial movement of said cam follower means and accordingly said positionable means; said cam face providing a relatively gradual axial movement of said positionable means throughout its major extent to correspond with said cooking operations; and providing substantially greater axial movement of said positionable means to a given position in its remaining extent to correspond with said cleaning operation.
 6. An oven and oven control system according to claim 5 wherein: said cam bushing includes means adjustable in an axial direction relative to said cam bushing at a location on said cam face to correspond with said cam follower means being in a cleaning operation position.
 7. An oven and oven control system according to claim 5 including: means for adjusting the position of said axially positionable means relative to said cam follower means independently of rotation of said cam follower means to permit calibration of said thermostat. 